The present invention relates generally to magnetic resonance imaging (MRI) devices, and more particularly to MRI devices with a removable keeper plate.
MRI devices are widely used in the medical community as a diagnostic tool for imaging items such as tissue and bone structures. As described, for example, in U.S. Pat. No. 5,680,086 (which is incorporated by reference herein in its entirety), a conventional MRI device may include opposing pole pieces which define between them an imaging volume for the item to be imaged, the pole pieces having pole plates which are fabricated from wound high permeability soft magnetic material, and/or laminated members. One conventional MRI manufacturing technique is described in European Patent Application EP 0 978 727 A2 (“EP '727” hereafter), filed on Jul. 22, 1999, which is incorporated by reference herein in its entirety.
In conventional MRI device manufacturing techniques, a yoke is assembled between two ends of the MRI device, and two pole pieces are positioned thereon with a gap provided underneath the pole piece at each end for the MRI magnet. The MRI magnet is then formed by pushing individual pre-magnetized permanent magnet blocks in place under the pole pieces on each end of the MRI device. Once all of the pre-magnetized permanent magnet blocks are positioned and secured in place, the pole pieces are lowered to their ultimate position and secured in place.
An MRI device manufactured by the aforementioned manufacturing technique, however, suffers from inclusion of a backing plate used to reinforce the pole pieces during the manufacturing process. Specifically, in the course of pushing the pre-magnetized permanent magnet blocks into place, the pole pieces must endure large bending forces due to the moving pre-magnetized permanent magnet blocks. A backing plate is used to overcome the bending forces by stiffening the pole pieces. The backing plate, however, affects the magnetic field generated by the permanent magnet block array. In highly precise MRI devices, this can lead to a degradation in the detection properties of the MRI device.
Thus, a need exists for a method of manufacturing an MRI device free of a backing plate in a pole face of the pole piece, and/or a method of manufacturing an MRI device with the pole pieces being subjected to a weaker and/or channeled magnetic fields during assembly.